The nerve growth factor protein (NGF) has been shown to be required for the differentiation of certain neuronal populations in the peripheral nervous systems. In addition, for sympathetic neurons, NGF is required for maintenance of the differentiated state. NGF has been purified and well characterized in mouse salivary gland and snake venom. In human tissues both determination of absolute levels of NGF and purification of an NGF molecule have been difficult to perform. Our laboratory has successfully isolated a beta-NGF molecule from placenta at term and developed a rocket immunoelectrophoretic assay for NGF. We plan to isolate the higher molecular weight form of human NGF from placenta at term and explore the degree to which this species is similar to murine or snake NGF.